Shortly after the start of his reign, Caligula embarked on a campaign which he hoped would lead to the conquest of Germany and Brittany, the details of which are not well known. The Legio XXII and XV were created and crossed the Alps in 39 AD towards the Rhine. During this campaign, the Primigenia most likely participated in the recovery of the eagles (ensigns) lost during the famous Teutoburg massacre.

From 43, the legion was stationed at Mogontiacum (now Mainz in Rhineland-Palatinate) in Upper Germania along with the Legio III Macedonica arriving from Spain. For their construction activities, the two legions jointly managed a center for the production of tiles and ceramics in Rheinzabern in the Palatinate.

An inscription found in Mainz indicates that between 43 and 70, 62% of the legionaries were from Italy, 33% from Gaul and 5% from Noricum.

Following the political unrest following the death of Neron where it had supported one of the losers, the Legio XXII Primigenia was then sent to the Danube in Pannonia and stationed at the Carnuntum camp (Petronell in Lower Austria). Not making the same mistake during a revolt of the Germanic legions, the XXII and all those who put down the rebellion of their brothers were awarded in 89 the title of Pia Fidelis (Loyale et Fidèle). It will be repositioned in Mainz three years later.

As the border armies developed, it became customary to detach certain units (vexillationes) to carry out temporary actions such as suppressing a rebellion or supporting another legion. Certainly renowned for the quality of its constructions, some of its units will be called upon with legionaries from Legio VII Gemina and Legio VIII Augusta to be part of the detachment (vexillatio) of some 1000 legionaries to build Hadrian's Wall in Grande -Brittany in 119.

The XXII Primigenia Pia Fidelis legion will remain in Mainz until the end of the Empire where it will experience the upheavals of politics and Christianity.

But this is another story...